DESCRIPTION: (Applicant's Abstract) The development of boron compounds for the treatment of squamous cell carcinoma of the head and neck (SCCHN) by Boron Neutron Capture Therapy (BNCT) requires the synthesis and evaluation of non-toxic agents which selectively target these malignant cells in contrast with adjacent normal tissue and are retained intracellularly. Cell membrane receptors mediating endocytotic transport of folic acid into cells are expressed in elevated levels in a variety of human tumors. The affinity of folic acid for its cell membrane receptors and its ability to be endocytosed remains essentially unaltered when a macromolecule is covalently linked to its gamma-carboxylate function. It has been shown that large numbers of conjugates of folic acid with therapeutic agents are internalized into tumor cells that overexpress the folate receptors by receptor-mediated endocytosis and are retained intracellularly. Therefore, folic acid may be an excellent carrier for the selective delivery of boron species to SCCHN. The specific aims of this proposal are: To develop the chemical methodology to design and synthesize suitable folic acid derivatives possessing 1 to 9 carborane and polyhedral borane clusters with or without a DNA-targeting entity. To prepare folic acid conjugates with boronated starburst dendrimers using polyethylene glycol spacers as binding elements. To synthesize and incorporate boronated polyamines into a liposomal formulation using folic acid-PEG-liposomes. To determine the in vitro uptake, persistence and subcellular distribution of boronated folic acid derivatives and liposomal formulations of boronated polyamines in human squamous cell carcinoma. To study the in vivo pharmacokinetics and tumor-localizing properties in tumor bearing rodents of those boronated folate derivatives and liposomal formulations of polyamines that show high in vitro cellular uptake and persistence. To evaluate the therapeutic efficacy for BNCT of those folic acid conjugates having favorable in vivo tumor-localizing properties.